1. Field of the Invention
The present invention relates to a method of treating semiconductor substrates by exposing the substrate to a hygroscopic liquid. The treatment minimizes the formation of voids in the fabricated semiconductor.
2. Description of the Related Art
During the fabrication of semiconductors and integrated circuits, it is often necessary to remove liquids such as water or solvents from the semiconductor or integrated circuit. For example, the semiconductor may be exposed to water through contact with aqueous solutions. At least a portion of the water is likely to remain on the semiconductor after the contacting. Alternatively, water may be formed as a reaction product during the chip fabrication. For example, U.S. Pat. Nos. 5,858,880 and 5,874,367 describe a method of planarizing wafers by forming silicon oxide films on the surface of the wafer by reacting silane with hydrogen peroxide to form silicon hydroxide. The silicon hydroxide polymerizes to form a gel containing water and polymers having the general formula Six(OH)y or SixHy(OH)z. More water is formed when the polymers are annealed to form the final SiO2 planarizing layer. The water is normally removed from the planarized wafer by heating.
Removing water from the wafer by heating can lead to structural problems in the wafer. For example, when the planarizing silicon hydroxide polymer gel layer described above is heated and annealed, the layer can crack if the rate of moisture removal is not controlled carefully during the phase transition from a gel to a solid. Controlling the rate of water loss can be achieved by careful temperature control, but this is expensive and time consuming. Alternatively, a silica capping layer can be formed on top of the wafer to control the rate of moisture release. Processing conditions must be controlled carefully to prevent cracking of the polymer layer. There is a need for more convenient and reliable methods of removing water during the processing of wafers.
The semiconductor or integrated circuit may also be exposed to solvents during processing. For example, spin-on layers are formed by spin applying silicon oxide, with or without dopants, in a solvent. The solvent is removed by baking, leaving a planarized SiO2 layer. The layer is subject to cracking during the drying process while the layer undergoes a phase change into a solid layer. There is a need for improved methods of removing solvents from semiconductor substrates without damaging the wafer.
One aspect of the invention relates to a method of removing at least a portion of a first liquid from a liquid-containing layer on a semiconductor substrate. The method comprises forming a first layer containing the first liquid on the semiconductor substrate, contacting the first layer with a second liquid which attracts the first liquid in the first layer, and transferring at least a portion of the first liquid from the first layer into the second liquid. The method also comprises separating the second liquid from the first layer, removing at least a portion of the first liquid from the first layer; and inducing a phase transition in the first layer. The phase transition may occur during or after the contacting.
Another embodiment of the invention comprises annealing the substrate and the first layer. Advantageously, the first layer undergoes the phase transition during the annealing.
Another aspect of the invention relates to a method of isolating plural trenches on a substrate. The method comprises placing the substrate in a chamber, introducing silicon-containing vapor and hydrogen peroxide vapor into the chamber, and reacting the silicon-containing vapor with the hydrogen peroxide vapor to form a liquid layer comprising silicon-containing oligomers and water on the substrate, where the liquid layer fills at least a portion of the trenches. The method also comprises contacting the liquid layer with a hygroscopic liquid to remove at least a portion of the water in the liquid layer, separating the hygroscopic liquid from the liquid layer, and heating the liquid layer to a temperature sufficient to form a solid comprising silica in at least a portion of the trenches.
In one embodiment, the silicon-containing vapor comprises silane. In some embodiments, the hygroscopic liquid is selected from sulfuric acid, phosphoric acid, and a hygroscopic organic solvent. Advantageously, the hygroscopic liquid comprises sulfuric acid. In an embodiment where the hygroscopic liquid comprises sulfuric acid, the hygroscopic liquid comprising sulfuric acid is contacted with the liquid layer at a temperature between 0 and 300xc2x0 Centigrade. In another embodiment, the hygroscopic liquid comprising sulfuric acid is contacted with the liquid layer at a temperature between 100 and 200xc2x0 Centigrade. In another embodiment, the hygroscopic liquid comprising sulfuric acid is contacted with the liquid layer at a temperature of approximately 150xc2x0 Centigrade.
In an embodiment of the invention, the hygroscopic liquid comprising sulfuric acid is at a concentration of between 50 and 98 weight percent sulfuric acid. In another embodiment, the hygroscopic liquid comprising sulfuric acid is at a concentration of approximately 98 weight percent sulfuric acid.
In an embodiment of the invention, the liquid layer is heated to a temperature between 100 and 1100xc2x0 Centigrade to form the solid comprising silica in at least some of the trenches. In another embodiment, the liquid layer is heated to a temperature between 300 and 800xc2x0 Centigrade. In yet another embodiment, the liquid layer is heated to a temperature of approximately 400xc2x0 Centigrade.
Another aspect of the invention relates to a method of treating a semi-conductor substrate. The method comprises: placing the substrate in a chamber, introducing silicon-containing vapor and hydrogen peroxide vapor into the chamber, reacting the silicon-containing vapor with the hydrogen peroxide vapor to form a liquid layer comprising silicon-containing oligomers and water on the substrate, and treating the liquid layer with a hygroscopic liquid, thereby removing at least a portion of the water in the liquid layer.
The method may further comprise separating the hygroscopic liquid from the liquid layer. In an embodiment of the invention, the method further comprises heating the liquid layer after separating the hygroscopic liquid from the liquid layer. Advantageously, the heating forms a solid comprising silica from the liquid layer.
In an embodiment of the invention, the solid comprising silica forms an interlayer dielectric layer on the substrate. Advantageously, the interlayer dielectric layer comprises a trench. The method may further comprise filling the trench with a metal. In an embodiment, the substrate comprises a plurality of trenches, and the solid comprising silica isolates the substrate between the trenches.
In another embodiment, the substrate comprises a plurality of metal lines on the substrate, and the solid comprising silica forms a dielectric layer over the plurality of metal lines.
In an embodiment of the invention, the silicon-containing vapor comprises methyl silane, and the liquid layer is heated to a temperature sufficient to convert then liquid layer to a solid comprising silicon oxide. Advantageously, the solid comprising silicon oxide forms a low-dielectric layer.
Another aspect of the invention concerns a method of treating a semiconductor substrate in a chamber. The method comprises applying a first liquid comprising silicon and a second liquid onto the substrate. The method further comprises contacting the first liquid comprising silicon and the second liquid with a third liquid which attracts the second liquid, removing at least a portion of the second liquid; and separating the third liquid from the first liquid comprising silicon on the substrate. In an embodiment, the second liquid comprises water and the third liquid comprises a hygroscopic liquid.
In an embodiment of the invention, the first liquid comprising silicon comprises silicon dioxide. In another embodiment, the first liquid further comprises a dopant selected from the group consisting of arsenic, antimony, boron, phosphorus, and gallium. In one embodiment, the applying comprises spin applying the first liquid comprising silicon and the second liquid onto the substrate. In another embodiment, the applying comprises chemical vapor depositing the first liquid comprising silicon and the second liquid onto the substrate.
In another embodiment, the applying comprises introducing silicon-containing vapor and hydrogen peroxide vapor into the chamber and reacting the silicon-containing vapor with the hydrogen peroxide vapor to form the first liquid comprising silicon and the second liquid, where the second liquid comprises water.
Another aspect of the method of the invention concerns a method of treating a semiconductor substrate in a chamber. The method comprises applying a first liquid onto the substrate and heating the substrate and the first liquid, thereby forming a second liquid and a third liquid. The method also comprises contacting the second liquid and the third liquid with a fourth liquid which attracts the third liquid, removing at least a portion of the second liquid, and separating the fourth liquid from the second liquid on the substrate.
In an embodiment of the method of the invention, the applying comprises spin applying the first liquid onto the substrate. In another embodiment, the first liquid comprises a siloxane or an organosiloxane. The third liquid advantageously comprises water, and the fourth liquid comprises higher oligomers of the siloxane or organosiloxane. The method may further comprise annealing the substrate and the fourth liquid, forming a layer comprising silicon dioxide.